Embossing roll with integral cooling means

ABSTRACT

A heat transfer roll, such as an embossing roll, for use in connection with systems for continuously advancing a length of flexible sheet material while the material is subjected to thermal treatment. The roll turns with a wrap of the sheet material that passes therearound, and has a thin-walled cylindrical outer shell and a tubular cylindrical core tightly fitted within the shell with passages for cooling fluid defined therebetween. The passages are defined by helical grooves formed in the outer surface of the core, that progress axially in a plurality of closely spaced helical convolutions. Cooling water, for example, is circulated through the passages to cool the roll surface and the sheet material.

Unite States atet [191 Bulson [75] Inventor: Douglas W. Bulson, Sylvania, Ohio [73] Assignee: The General Tire & Rubber Company, Akron, Ohio [22] Filed: Jan. 6, 1972 [21] Appl. No.: 215,746

[52] US. Cl. 165/89 [51] Int. Cl. F281) 13/06 [58] Field of Search..... 165/89, 90

[56] References Cited UNITED STATES PATENTS 3,419,068 12/1968 Grierson 165/89 2,661,545 12/1953 Messinger.... 165/89 2,793,006 5/1957 Eaby 165/89 Aug. 14, 1973 Primary ExaminerCharles J. Myhre Assistant ExaminerTheophil W. Streule, Jr. Attorney-McCoy, Greene & Howell [5 7] ABSTRACT A heat transfer roll, such as an embossing roll, for use in connection with systems for continuously advancing a length of flexible sheet material while the material is subjected to thermal treatment. The roll turns with a wrap of the sheetmaterial that passes therearound, and has a thin-walled cylindrical outer shell and a tubular cylindrical core tightly fitted within the shell with passages for cooling fluid defined therebetween. The passages are defined by helical grooves formed in the outer surface of the core, that progress axially in a plurality of closely spaced helical convolutions. Cooling water, for example, is circulated through the passages to cool the roll surface and the sheet material.

3 Claims, 6 Drawing Figures Patented Aug. '14, 1973 EMBOSSING ROLL WITH INTEGRAL COOLING MEANS BACKGROUND OF THE INVENTION This invention relates to systems for heat treating lengths of flexible sheet material and especially to the construction of rolls that have a wrap of the sheet material passed therearound, and that turn with the advancing material. More particularily, the invention relates to the construction of rolls such as embossing rolls that have a heat transfer medium circulated therethrough to cool heat softened thermoplastic material that is embossed by a textured roll surface and simultaneously cooled to set the embossed pattern in the sheet material.

Conventional embossing rolls are large hollow cylinders, usually about feet long, with an outer surface etched with a negative design or texture for the desired surface finish. The wall of the cylindrical roll has con-' ventionally been about one inch thick and a plurality of longitudinal holes are drilled therethrough parallel to the roll axis to provide passages for cooling water. Because of the thickness of the wall of the roll, however, prior art constructions have a relatively low rate of heat transfer so that the roll speeds are considerably limited during the embossing operation. Also in prior art rolls the liquid cooling medium flows from one end to the other so that heat transfer is not uniform across the roll surface. Normally more heat transfer is required at the center of the roll.

If the roll becomes too hot, the impression of the roll surface will not be permanently embossed in the thermoplastic material since it will not take a permanent set unless cooled to below a setting temperature during the period that it is in contact with the embossing roll surface.

Another disadvantage with prior art roll constructions is that when the embossing design on the roll surface became obsolete, the entire roll must be scrapped, thus greatly limiting the utility of an extremely costly piece of equipment.

The heat transfer roll construction of the present invention, however, resolves the difficulties and disadvantages indicated above, provides for substantially higher roll speeds, and affords other features and advantages not obtainable from the prior art.

SUMMARY OF THE INVENTION It is among the objects of the invention to control more uniformly the temperature of a heat transfer roll by circulating a heat transfer liquid through the roll adjacent the outer surface.

Another object is to improve the efficiency of heat transfer in water cooled embossing rolls.

Still another object is to increase the speeds of operation of water cooled embossing rolls for texturing or patterning the surface of heat softened thermoplastic material.

A further object is to provide an improved construction for a water cooled embossing roll wherein a portion of the roll with the textured forming pattern etched therein can be replaced-on other structural parts of the roll so as to eliminate the need for scrapping the entire roll when the embossing surface becomes damaged or worn.

These and other objects and advantages are accomplished by means of a heat transfer roll of the type described, for use in association with a system that continuously advances and thermally treats a length of flexible sheet material, the roll being adapted to receive a wrap of the sheet material therearound and to turn at a surface velocity corresponding to the linear velocity of the sheet material, and comprising in accordance with the invention, a tubular cylindrical core and a thin-walled cylindrical outer shell tightly fitted around the core. The core has helical grooves formed in its outer surface including at least one groove on each side of a central circumferential plane thereof, each groove progressing axially from the central plane in a plurality of closely spaced helical convolutions about the core to its respective end of the core.

The thinwalled cylindrical outer shell is tightly fitted around the core so that its inner surface defines with the outer surface of the core, enclosed helical passages extending from the middle portion of the roll to the ends thereof. Water is supplied to the helical passages from inside the middle portion of the roll and circulated from the middle portion of the roll progressively through the helical passages to the respective ends thereof to maintain a desired uniform temperature on the surface of the roll.

According to the preferred embodiment the cooling water is supplied from an axial inlet pipe through a rotary coupling to the interior of the core and from the interior of the core through radial ports to a central annular groove between the core and the shell, that communicates with the helical grooves that progress in opposite directions from the central groove progressively toward the opposite ends. At the very ends of the grooves the cooling water is directed through one or more radial ports to axial outlet passages in each end of the roll.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a diagram of an apparatus for continuously advancing and embossing a length of thermoplastic sheet material;

FIG. 2 is an elevational view of an embossing roll with internal cooling means, for the apparatus of FIG. 1;

FIG. 3 is a sectional view on an enlarged scale of the embossing roll of FIG. 2 taken on the line 3-3 of FIG. 1, with parts broken away and shown in section for the purpose of illustration;

FIG. 4 is a transverse cross section taken on the line 44 of FIG. 3;

FIG. 5 is a transverse cross section taken on the line S5 of FIG. 3; and

FIG. 6 is a transverse cross section tkaen on the line 6-6 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring more particularly to the drawings and initially to FIG. 1, there is shown in diagrammatic form, an apparatus for continuously advancing, heat softening and embossing a length of flexible thermoplastic sheet material 10 that is fed from a supply reel 11 and delivered in embossed condition to a take-up reel 12. From the supply reel 11 the thermoplastic sheet material 10 passes. from an idler roll 13 to a heater roll 14 wherein by contact with the heated surface of the roll it is heated to a heat softened condition. the heater theheater roll 14 the material is advanced to an embossing roll 15 that embosses a textured surface finish in the heat softened thermoplastic material and cools the ma terial sufficiently to provide a permanent set of the embossed pattern in the surface. From the emobssing roll 15 the embossed material passes around an idler roll 16 and to the take up reel 12.

According to the invention, the embossing roll 15 is formed to provide an exceptionally efficient heat transfer to cool the heat softened material as the textured surface finish is embossed therein and thus provide for advantageously fast roll speeds. The roll 15 comprises a tubular cylindrical core 20 (FIG. 3) formed for example from solid steel or cast iron cylindrical stock, located within a thin walled cylindrical outer shell 21 that has its outer surface etched with the negative pattern or texture of the surface finish to be embossed in the plastic material.

The ends of the core 20 are closed with end plugs 22 and 23 respectively to define within the core a cylindrical inner space 24. Water is introduced into the cylindrical space through an axial inlet pipe 25 that is connected for example through a rotary coupling (not shown) so as to accomodate the turning of the roll about its axis. The outer end portions 26 and 27 of the end plugs 22 and 23 are machined to provide journal surfaces that turn in bearings (not shown) so that theroll may rotate freely at the same surface speed as the speed of translation of the plastic sheet material. The take up reel 12 is provided with drive means to advance the material at a desired linear speed.

Formed in the middle of the core 20 on its outer surface is a central annular groove 30 asindicated in F108. 3 and 5. The groove communicates with the inner space 24 through four symmetrically spaced central radial ports 31. The opposite ends of the core 20 are also provided with annular grooves 32' and 33 respectively (FIGS. 3, 4 and 6), that are spaced slightly from the outer ends of the core. Four symmetrically spaced radial ports 34 extend from the groove 32 inwardly through the core 20 and through the end plug 22 to an axial passage 35. Four other radial ports 36 extend from the annular end groove 33 inwardly through the core 20 and through the end plug 23 to an axial outlet passage 37 in the end plug 33. The axial passage 37 also receives through the central portion thereof the axial inlet pipe 25. The inlet pipe 25 is threaded into a threaded opening 38 at the innermost portion of the end plug 23 as indicated in FIG. 3.

Formed in the outer surface of the core 20 between the central annular groove 30 and the annular end groove 32 are four closely spaced helical grooves 41, 42, 43 and 44, that extend from right to left as viewed in FIG. 3, in a plurality of closely spaced helical convolutions about the core. Formed in the core 20 between the central annular groove 30 and the annular end groove 32 are four other helical grooves 51, 52, 53 and 54 extending from left to right as viewed in FIG. 3 in a plurality of closely spaced helical convolutions. The helical grooves 41, 42, 43 and 44 have an opposite thread and hand of lay from the helical grooves 51, 52, 53 and 54 and the convolutions respectively of all the channels are spaced as closely as possible to the next adjacent convolution so that the roots of the reslting threads are as wide as possible while the crests resulting of minimum size. The grooves are formed by a conventional machining operation preferably to have a curved circular cross section as indicated in FIG. 3, however, other groove shapes can also be used to advantage.

The cylindrical outer shell 21 is heat shrunk on to the core 20 so that the inner surface of the shell 21 defines with the helical grooves 41-44 and 51-54, helical passages for the circulation of cooling water. it will be seen that a major portion of the inner surface of the shell 21 is in contact with cooling fluid in the helical passages so that an optimum heat transfer from the thin shell wall to the cooling water is provided. While the shell 21 has a very small wall thickness and thus little rigidity by itself. The crests of the helical grooves provide adequate support for shell wall thicknesses as small as about one-fourth inch for example. It will be apparent that the thinner the wall thickness the greater the heat transfer from the shell to the cooling fluid.

As indicated above the cooling water to be circulated through the wall is introduced through the axial inlet pipe 25 through a rotary coupling (not shown) to the inner space 24 within the core 20. This water is then circulated radially outwardly through the central radial ports 31 to the central annular groove 30. With the groove 30 the water moves in opposite directions, on the one hand, to the four channels defined by the helical grooves 41 to 44 at the left hand side of the central groove 30 as viewed in FIG. 3, and on the other hand, to the four channels defined by the helical grooves on the right hand side of the roll 15 as viewed in FIG. 3. Thus the water passes initially in arelatively cooler state from the center of the roll 15 progressively to the ends thereof to maintain a desired temperature at the surface of the roll. With this arrangement the most efficient heat transfer is provided at the center of the roll 15 rather than at the ends as is the case with embossing rolls of the prior art. When the cooling water reaches one of the respective annular end grooves 32 and 33, it is circulated through the radial ports 34 on the one hand or the radial ports 36 on the other hand to one of the axial passages 36 and 37. From there it passes outwardly in axial directions preferably through rotary couplings, to be discharged.

According to one aspect of the invention wherein the outer shell 21 has a minimum wall thickness, say for example, one-fourth inch, some difficulty may be experienced in etching the desired surface texture on the outer surface of the shell 21 in view of the fact that there may be insufficient rigidity for the shell. This difficulty can be overcome by filling the roll with water under pressure such as for example 60 pounds per square inch so as to improve the rigidity of the shell and facilitate the etching operation.

When the embossing texture or pattern in the shell surface becomes obsolete or damaged, the shell may be removed from the core and scrapped while the core may be provided with another shell and reused indefinitely.

While the invention has been shown and described with respect to a specific embodiment thereof this is for the purpose of illustration rather than limitation and other variations and modifications of the specific device herein shown and described will be apparent to those skilled in the art, all within the intended spirit and scope of the invention. Accordingly the patent is not to be limited in scope and effect to the specific embodiment herein shown and described nor in any other way that is inconsistant with the extent to which the progress in the art has been advanced by the invention.

I claim:

1. In apparatus for continuously advancing and embossing while heat softened, a length of flexible thermoplastic sheet material, an embossing roll with an etched outer surface and integral cooling means, adapted to receive a wrap of said advancing heat softened sheet material therearound and to turn at a surface velocity corresponding to the linear velocity of said advancing length, to emboss and cool said length, said roll comprising:

a tubular inner cylinder having helical grooves formed in the outer surface thereof including at least one groove on each side of a central circumferential plane thereof, each surface progressing axially from said central plane in a plurality of closely spaced helical convolutions about said inner cylinder to the respective end of said inner cylinder,

a thin-walled cylindrical outer shell removably fitted around said inner cylinder, the outer surface thereof being an embossing die for heat softened plastic sheet and the inner surface thereof defining with said inner cylinder, enclosed helical passages extending from the middle portion to the ends of said roll,

means for closing and sealing the ends of said inner cylinder to define therewithin an enclosed cylindrical chamber adapted to contain a relatively large volume of liquid coolant, and

means for supply liquid coolant through said closing and sealing means for said chamber, then to the inner ends of said helical passages and through said passages to the outer ends thereof to cool said outer shell and to maintain said shell at a desired temperature for setting said embossed pattern in said sheet, and for discharging said liquid coolant through said closing and sealing means from the outer ends of said passages.

2. A heat transfer roll as defined in claim 1 wherein said core has a central annular groove and wherein the inner ends of said passages terminate at said annular groove.

3. A heat transfer roll as defined in claim 2 wherein each helical passage on one side of said annular groove has an opposite hand of lay from each helical passage on the opposite side of said annular groove 3 UNITED STATES PATENT OFFICE fiERTIFTCATE 0F CORRECTION Patent No. 3 ,752, 27 Dated Aug 973 Inventor(s) Douglas Wo Bulson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2 line 5A, "tkaen" should be --taken-. Column 3, line 1, the heater should be --From--. Column 3, line 67, resulting should be --are-- Column L, line 2 4, "With" should be --From- Add the following claim:

L. A heat transfer roll as defined in claim 1 wherein four helical passages are provided on each side of said central circumferential plane, said four passages having the same pitch and hand of lay and having their convolutions closely spaced to the convolutions of the respective adjacent passages.

Signed and sealed this 18th day of December 1973.

(SEAL) Attest:

EDWARD M. PLETCHER,JR. RENE n. TEGTMEYER Attesting Officer Acting Commissioner of Patent 

1. In apparatus for continuously advancing and embossing while heat softened, a length of flexible thermoplastic sheet material, an embossing roll with an etched outer surface and integral cooling means, adapted to receive a wrap of said advancing heat softened sheet material therearound and to turn at a surface velocity corresponding to the linear velocity of said advancing length, to emboss and cool said length, said roll comprising: a tubular inner cylinder having helical grooves formed in the outer surface thereof including at least one groove on each side of a central circumferential plane thereof, each surface progressing axially from said central plane in a plurality of closely spaced helical convolutions about said inner cylinder to the respective end of said inner cylinder, a thin-walled cylindrical outer shell removably fitted around said inner cylinder, the outer surface thereof being an embossing die for heat softened plastic sheet and the inner surface thereof defining with said inner cylinder, enclosed helical passages extending from the middle portion to the ends of said roll, means for closing and sealing the ends of said inner cylinder to define therewithin an enclosed cylindrical chamber adapted to contain a relatively large volume of liquid coolant, and means for supply liquid coolant through said closing and sealing means for said chamber, then to the inner ends of said helical passages and through said passages to the outer ends thereof to cool said outer shell and to maintain said shell at a desired temperature for setting said embossed pattern in said sheet, and for discharging said liquid coolant through said closing and sealing means from the outer ends of said passages.
 2. A heat transfer roll as defined in claim 1 wherein said core has a central annular groove and wherein the inner ends of said passages terminate at said annular groove.
 3. A heat transfer roll as defined in claim 2 wherein each helical passage on one side of said annular groove has an opposite hand of lay from each helical passage on the opposite side of said annular groove. 